As a wind power generation device that performs power generation by rotating the main shaft by the blade receiving wind, a device having a speed-up gear is available. This speed-up gear increases the rotation speed of the main shaft so that the power generator is driven.
As shown in FIG. 8, a speed-up gear 202 is provided with a planet gear mechanism 203 that receives the rotation of a main shaft 200 and increases its speed, a high-speed stepped gear mechanism 204 that receives the rotation increased in speed by this planet gear mechanism 203 and further increases the speed of the rotation, and an output shaft 205 that outputs the rotation increased in speed by this high-speed stepped gear mechanism 204. To this output shaft 205, the drive shaft (not shown) of the power generator is coupled, and to this drive shaft, the rotor of the generator is attached.
In the planet gear mechanism 203, when an input shaft 203a rotates that is integrally rotatably coupled to the main shaft 200 to which the non-illustrated blade is attached, a planet carrier 203b rotates, whereby a sun gear 203d is rotated with increased speed through a planet gear 203c. Then, this rotation is transmitted to a low-speed shaft 204a of the high-speed stepped gear mechanism 204.
In the high-speed stepped gear mechanism 204, when the low-speed shaft 204a rotates, an intermediate shaft 204d is rotated with increased speed through a low-speed gear 204b and a first intermediate gear 204c, and further, the output shaft 205 is rotated with increased speed through a second intermediate gear 204e and a high-speed gear 204f. 
And in this speed-up gear 202, as the bearings that rotatably support the low-speed shaft 204a, the intermediate shaft 204d and the output shaft 205, rolling bearings (roller bearings) 206 to 211 are frequently used (for example, see Patent Document 1).